The present invention related generally to router bits for forming a workpiece, and more particularly to bits of this type that are designed to form tongues and grooves in the workpiece.
As is well known in the art, when it is desired to cut a groove or a corresponding tongue into the side face of a wooden workpiece, a rotating bit is provided which includes two cutter elements fixed onto a drive shaft, and the rotating bit is moved laterally into contact with the edge of the workpiece to be formed. If the workpiece is to be formed with a tongue, the bit includes two cutter members fixed thereon at a spacing corresponding to the thickness of the tongue to be formed so that the edge of the workpiece is cut away by the cutter elements above and below the portion that becomes the tongue. Similarly, if the workpiece to be formed is a groove, the bit includes a single cutter member having a thickness corresponding to the desired thickness of the groove.
In either event, each of the cutter elements is fixed to the drive shaft, and therefore each bit can only cut a tongue or groove having one specific thickness. Therefore, in applications where it is necessary to form workpieces with grooves and tongues having varying thicknesses, it is necessary to have in stock a large inventory of bits, each being capable of cutting one groove or tongue thickness within the range of desired thicknesses. Obviously, this can significantly increase the expense of the workshop in acquiring and maintaining the required number of bits that may be necessary for the particular operations of the workshop.
It is also known to provide a drive shaft onto which any one of a number of different sized cutter members can be secured in fixed relation to one another to thereby vary the thickness of the tongue or groove to be formed by the bit. In this arrangement, each of the cutter members has a fixed axial thickness, and when the thickness of the tongue or groove to be formed is determined, the operator selects the two particular cutter members that will provide the desired thickness, and then mounts these two cutter members on the drive shaft.
This arrangement is an improvement over the above-described practice of maintaining a large number of different bits in stock, but it also has a similar disadvantage in that it requires the workshop to maintain in inventory a large number of cutter elements of varying sizes that can be mounted on the drive shaft to form a tongue or groove of a desired thickness.
Additionally, this arrangement has a further disadvantage in that the size of the replaceable cutter members makes it difficult for any two of them to be mounted on the drive shaft with the required axial tolerance needed to form a tongue or groove of a specific axial thickness.
The present invention provides an adjustable bit for cutting tongues or grooves in a wooden workpiece which includes an axially extending drive shaft, a first cutter member mounted on the drive shaft and movable along the axial length thereof, and a second cutter member mounted on the shaft and movable along the axial length thereof A plurality of spacer elements are selectively mountable on the shaft intermediate the first and second cutter members to vary the axial spacing therebetween. A cap member is removably mounted on the drive shaft to permit at least one of the cutter members to be mounted on and removed from the shaft, and to permit one or more of the spacer elements to be mounted on and removed from the shaft, and the cap member has a fixed position thereon for holding in place the first and second cutter members and the spacer elements therebetween, whereby the adjustable bit can be used to cut grooves or tongues of varying thicknesses in the workpiece.
In one of the preferred embodiments, at least some of the spacer elements have different axial thicknesses, and there may be nine of the spacer elements mountable on the drive shaft, with some of the spacer elements having the same axial thickness and some of the spacer elements have axial thicknesses which are different from other spacer elements. More particularly, it is preferred that four of the spacer elements have an axial thickness of 1 mm; two of the spacer elements have an axial thickness of 0.2 mm; and three of the spacer elements have an axial thickness of 0.5 mm, 0.15 mm and 0.1 mm, respectively.
It is also preferable that the cutter members, the spacer elements and the cap member be stacked on the drive shaft with the first cutter members being in the lowermost position, with at least some of the spacer elements on top of the first cutter member, with the second cutter members being on top of the spacer elements, and with the cap member fixed in place on the shaft above the second cutter member. However, the spacer elements may be arranged so that some of them are located between the first and second cutter members to provide the desired spacing therebetween, and any remaining spacer elements can be conveniently carried above the second cutter member and between the second cutter member and the cap member.
In one embodiment of the present invention, the first and second cutter members are formed to cut a tongue in the workpiece. In this embodiment, the spacer elements preferably include a ball bearing pilot member disposed between the first and second cutter members to provide a guide surface for the workpiece as it is being cut by the adjustable bit, and the spacer elements also include a plurality of shims, at least some of which are mounted on the drive shaft between the ball bearing pilot member and at least one of the first and second cutter members.
In another embodiment of the present invention, the first and second members are formed to cut a groove in the workpiece, and in this embodiment the first and second cutter members are provided with cutting blades that are capable of overlapping one another in the axial direction whereby grooves of different depths can be cut using the same cutter members and the aforesaid spacer elements.